I just came across this while researching another piece on David Cameron. How apposite, it seems:

We are in a war of a peculiar nature. It is not with an ordinary community, which is hostile or friendly as passion or as interest may veer about: not with a state which makes war through wantonness, and abandons it through lassitude. We are at war with a system, which by its essence, is inimical to all other governments, and which makes peace or war, as peace and war may best contribute to their subversion. It is with an armed doctrine that we are at war. It has, by its essence, a faction of opinion, and of interest, and of enthusiasm, in every country.

The author? Edmund Burke – Letters on Regicide Peace, 1796.